Business Segments (Operating Results and Other Key Financial Measures) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Total Segment Reporting Information
Interest income	$ 463,311	$ 371,873
Charge for funds used	(216,772)	(178,966)
Interest spread on funds used	246,539	192,907
Interest expense	(100,850)	(45,180)
Credit on funds provided	216,772	178,966
Interest spread on funds provided	115,922	133,786
Net interest income before provision for credit losses	362,461	326,693
Provision for credit losses	22,579	20,218
Noninterest income	42,131	74,444
Noninterest expense	186,922	169,135
Segment income before income taxes	195,091	211,784
Segment net income	164,024	187,032
Segment assets	42,091,433	37,671,938	$ 41,042,356
Consumer and Business Banking
Total Segment Reporting Information
Interest income	134,339	104,710
Charge for funds used	(77,446)	(49,273)
Interest spread on funds used	56,893	55,437
Interest expense	(55,709)	(24,940)
Credit on funds provided	165,004	145,451
Interest spread on funds provided	109,295	120,511
Net interest income before provision for credit losses	166,188	175,948
Provision for credit losses	3,013	3,093
Noninterest income	13,772	44,448
Noninterest expense	87,906	87,317
Segment income before income taxes	89,041	129,986
Segment net income	63,655	93,134
Segment assets	10,902,961	9,327,355
Commercial Banking
Total Segment Reporting Information
Interest income	296,140	239,577
Charge for funds used	(162,625)	(111,366)
Interest spread on funds used	133,515	128,211
Interest expense	(23,650)	(9,179)
Credit on funds provided	37,375	25,448
Interest spread on funds provided	13,725	16,269
Net interest income before provision for credit losses	147,240	144,480
Provision for credit losses	19,566	17,125
Noninterest income	24,544	27,438
Noninterest expense	70,544	61,302
Segment income before income taxes	81,674	93,491
Segment net income	58,499	67,029
Segment assets	23,964,592	22,002,393
Other
Total Segment Reporting Information
Interest income	32,832	27,586
Charge for funds used	23,299	(18,327)
Interest spread on funds used	56,131	9,259
Interest expense	(21,491)	(11,061)
Credit on funds provided	14,393	8,067
Interest spread on funds provided	(7,098)	(2,994)
Net interest income before provision for credit losses	49,033	6,265
Provision for credit losses	0	0
Noninterest income	3,815	2,558
Noninterest expense	28,472	20,516
Segment income before income taxes	24,376	(11,693)
Segment net income	41,870	26,869
Segment assets	$ 7,223,880	$ 6,342,190